I'm not an admirer of Rowan Williams as a prose stylist, but just for fun I tried to read the passage held up for ridicule by Terry Sanderson. It seems to make sense. Theology, says Rowan, is not the study of God, who can't be pinned down for study ("his word is not bound"). It's not even the study of what God has done. Instead theology is language to make us aware what a huge task that study would be, because the awareness of that immensity is the beginning of the work and study of some small details is as far as we can ever get into it. This, he says, is also the method of St John's gospel.

That seems perfectly comprehensible, whether or not it is true. It also implies something important about the distinction between theology and science: the purpose of scientific investigation is to produce reliable third-party knowledge which would be true even if there were no one to know it. But the purpose of Christian theology is to change the theologians. The knowledge it results in would then be inward, personable, and as incommunicable as any other aspect of experience.

The interesting question is whether it can then be classed as knowledge at all.

Lots of people here would claim that it could not, and that personal experience is worthless compared to measurable fact. But if you take that argument seriously – and I can see that it has charms for anyone who finds aspects of personal experience unbearable –it would lead to shutting down a lot more of universities than their theology departments. There would be no reason to teach ethics – where's the verifiable truth there? – or literature or even aesthetics more generally. Narrative history would have to go. Economics would have all the people taken out of it in favour of hard safe numbers. That last experiment has of course been tried with the results we see all around us.

It's easy to carry the distinction between knowledge and experience too far. But I think that we can't live without personal and incommunicable knowledge. The stories we tell ourselves and the lessons we have learned from life are an example. Of course these can be full of self-deception and probably are. But the mere fact of self-deception implies the possibility of its opposite, self-knowledge.